U.S. patent number 3,969,699 [Application Number 05/567,154] was granted by the patent office on 1976-07-13 for image dissector with many apertures for hadamard encoding.
This patent grant is currently assigned to Honeywell Inc.. Invention is credited to Laurence D. McGlaughlin.
United States Patent |
3,969,699 |
McGlaughlin |
July 13, 1976 |
Image dissector with many apertures for Hadamard encoding
Abstract
An improved image dissector camera tube system for improving the
signal-to-noise ratio in which the aperture plate of the image
dissector has a plurality of apertures, the apertures individually
biased by an electronic control network to accomplish a Hadamard
encoding of the electron image.
Inventors: |
McGlaughlin; Laurence D.
(Edina, MN) |
Assignee: |
Honeywell Inc. (Minneapolis,
MN)
|
Family
ID: |
24265941 |
Appl.
No.: |
05/567,154 |
Filed: |
April 11, 9175 |
Current U.S.
Class: |
382/281; 250/207;
313/381; 382/324; 708/820; 313/103R; 315/11 |
Current CPC
Class: |
H01J
29/98 (20130101); H01J 31/42 (20130101) |
Current International
Class: |
H01J
29/98 (20060101); H01J 31/42 (20060101); H01J
29/00 (20060101); H01J 31/08 (20060101); H01J
039/12 () |
Field of
Search: |
;315/10,11,365 ;250/207
;313/65R,13R ;340/146.3F,146.3G,146.3MA,146.3SY ;235/164,197 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Decker, "Hadamard-Transform Image Scanning," Applied Optics, vol.
9, No. 6, June, 1970. pp. 1392-1395. .
ETT, "Character Recognition Image Dissector," IBM Tech. Disclosure
Bulletin, vol. 12, No. 9, Feb. 1970. pp. 1339-1340..
|
Primary Examiner: Boudreau; Leo H.
Attorney, Agent or Firm: Dahle; Omund R.
Claims
The embodiments of the invention in which our exclusive property or
right is claimed are defined as follows:
1. An improved image dissector camera tube system comprising:
photocathode means for generating an electron image;
a plurality of normally operative detector means at known adjacent
positions of the electron image for producing signals indicative of
the electron density at each of the known adjacent positions;
electron controlling means for causing one of a plurality of
predetermined patterns of said plurality of detector means to be
inoperative during each of a plurality of successive image sampling
periods, said electron controlling means further comprising
programmed modulator means connected in controlling relation to
each of said detector means;
combining means for combining the signals from the operative
detector means during each of the plurality of sampling periods to
produce a combined signal for each of said plurality of periods,
said programmed modulator means together with said combining means
being so coded as to cause the electron image to be transformed to
a Hadamard image; and
transform means for transforming the combined signals into a series
of electrical signals indicative of the electron image.
2. The system according to claim 1 wherein said transform means is
an inverse Hadamard transform means.
3. An improved image dissector camera tube system comprising:
photocathode means for generating an electron image;
n normally operative detector means at known adjacent positions of
the electron image for producing signals indicative of the electron
density at each of the known adjacent positions;
where n is an integer;
electron controlling means for causing a different one of n
predetermined patterns of said detector means to be inoperative
during each of n successive image sampling periods;
combining means for combining the signals from the operative
detector means during each of the n sampling periods to produce a
combined signal for each of said periods, said electron controlling
means further comprising programmed modulator means connected in
controlling relation to each of said detector means, said
programmed modulator means together with said combining means being
so coded as to cause the electron image to be transformed to a
Hadamard image; and
transform means for transforming the combined signals into a series
of electrical signals indicative of the electron image.
Description
BACKGROUND OF THE INVENTION
Image dissector type television camera tubes are a well-known,
non-storage type of camera tube that utilizes a photoemissive
light-sensitive surface. The tube has been described as one which
does not have a scanning beam but which collects and directly
amplifies the electron image emitted from the photosensitive
surface. The image being viewed by the camera is focused on a
transparent photoemissive surface on the inside of the camera tube.
Electrons are emitted from all areas on the photosurface in
densities which are a function of the brightness of the image at
that location. The electron image is conveyed as a whole to the
opposite end of the tube where it encounters an electrode or plate
having a small aperture. Under the control of external magnetic
deflection coils or electric deflection plates, the electron image
is deflected past this aperture so that the image is explored by
the aperture in a series of horizontal adjacent lines. As a result,
the aperture periodically samples the entire photoelectric image.
The electrons which enter the aperture constitute the current
impulses corresponding to the successive values of brightness
passing by the aperture. The electrons entering the aperture are
multiplied by secondary emissions of the multiplier dynodes. The
electrons that do not pass through the aperture are not utilized.
Since no charge storage occurs in the image dissector, its
sensitivity is low. Conventional image dissector tubes receive
electrons through only one aperture, that is, from only one element
of the scene at a time. The use of multiple apertures has been
considered in the prior art. Several such examples are U.S. Pat.
Nos. 3,274,581, 3,333,145 and 3,720,838.
SUMMARY OF THE INVENTION
In this invention a plurality of apertures are used in an image
dissector tube. This multiple aperture plate together with
electronic programmed modulator apparatus means such as a prewired
switching sequence generator for selectively controlling and
switching the multiple apertures, establishes an electronic pattern
which will accomplish encoding of the image, thus permitting the
image dissector tube to integrate over a longer dwell time for each
image element while maintaining the same frame time thus providing
a higher signal-to-noise ratio. Further electronic apparatus for
solving the coding provides a greatly improved image.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 discloses a conventional image dissector television camera
tube such as is known in the prior art;
FIG. 2 shows an image dissector tube having a plurality of
apertures in the aperture plate;
FIG. 3 is a representation of the multiplier dynodes which are
positioned behind the aperture in an image dissector tube and FIG.
3a is a perspective view of one of the dynodes;
FIG. 4 is an enlargement of a portion of the aperture plate
area;
FIG. 5 is a system block diagram of the improved image dissector
tube and the associated control apparatus;
FIG. 6 is a representation of an image in graphical/numerical
form;
FIG. 7 is a representation of one set of aperture voltages used to
provide a Hadamard image;
FIG. 8 is a graphical/numerical representation of a Hadamard image
produced from the image of FIG. 6;
FIGS. 9 and 10 are optical mask analogies of Hadamard transform
encoders;
FIGS. 11, 12, and 13 show the coding at various scan positions;
FIG. 14 describes the transform S;
FIG. 15 describes the inverse of the transform S.sup.-.sup.1 ;
FIG. 16 shows the transpose of the inverse of the transform
(S.sup.-.sup.1).sup.T ; and
FIGS. 17a and 17b are an example of the solution of the transform
by the apparatus of FIG. 5.
DESCRIPTION
FIG. 1 discloses in simplified form a conventional image dissector
television camera tube, such as is well-known in the art, the image
dissector employing a photosensitive cathode 12 which does not
store a charge but which liberates an electron image when
illuminated by the optical image 10 focused on it. The electron
image 15 so produced is conveyed as a whole to the opposite end of
the tube. The electron image is deflected past an aperture 16 so
that the entire image is explored by the aperture in a series of
sweep lines. The electrons which enter the aperture constitute the
current impulses corresponding to the successive values of
brightness passing by the aperture. The electron current entering
the aperture is multiplied by the multiplier dynodes 17 before
providing a signal output 18.
In the present invention the image dissector camera tube as shown
in FIG. 2 is modified to provide a large number of apertures 16' in
the aperture plate rather than one aperture as is common. Many
elemental bits of the electron image are thus seen at one time by
the apertures. The many apertures are biased selectively so as to
feed the electron picture through the many apertures in different
parallel combinations to accomplish Hadamard encoding of the scene.
This permits the image dissector tube to integrate over a longer
dwell time for each image element while maintaining the same frame
time thus providing a higher signal-to-noise ratio. The average
improves with the square root of the viewing time.
For illustrative purposes, the multiple aperture arrangement has
been shown as a 7 .times. 7 array of 49 apertures, 16'. There is no
significance in the choice of a 7 .times. 7 array other than
convenience of explanation, and any suitable size array may be
used. Behind the aperture array 16' is a conventional dynode
multiplier such as is shown in FIG. 3 in which the electrons
flowing through the multiple apertures are summed in a common
dynode multiplier.
FIG. 4, an enlargement of a portion of the multiple aperture plate,
shows an embodiment of how the individual apertures are selectively
biased. A non-conductive substrate 20 having the grid of 49
apertures therein, has an evaporated film of aluminum, or other
metal, surrounding each aperture, the metalized areas being
identified as 21, 22, 23, and 24 and having separate metalized
leads 25 through 28 to which external connection is made. The
individual apertures have a diameter of about 3 to 4 mils, and spot
welded to the metalized areas across the apertures are control
wires such as shown at 30, 31, 32, and 33. Each aperture with its
metalization and control wire is insulated from the other 48
apertures.
In the system block diagram of FIG. 5, a programmed modulator 34
has electrical connection 35 to the plurality of apertures 16'. The
programmed modulator is preferable in the form of a prewired
switching sequence generator and switches the aperture grid in the
same way one addresses n different memory locations in a random
access memory. The electrical connection 35, shown schematically
simplified, includes a separate electrical connection to each of
the multiple apertures. The apertures may be thought of as
controllable gates or windows and electrical potentials applied to
the apertures from the programmed modulator 34 open or close each
gate to electrons. Each of the 49 apertures may be considered as
detector means for the electron image. The detector means are
controllable electron density responsive means. There are also 49
different combinations or different patterns of aperture gating
applied by the sequential application of a series of programmed
bias control voltages to the apertures. In this way, the detectors
are caused to view the same image n times while sequencing through
the n combinations thereby to generate a Hadamard image.
Let it be assumed that a stationary image is being observed which
results in an electron image as shown in FIG. 6 in the form of an
H. The numerical values forming the H represent relative electron
intensities. Both dimensions of the deflection, i.e. the vertical
and horizontal deflection, as applied by the deflection coils 14
may be in the form of stairstep increments so that the portion of
the image in the view of the 7 .times. 7 apertures remains in
position long enough for the programmed modulator system to view
(i.e. electronically scan) the image portion illustrated as H 49
times.
FIG. 7 gives an example of the aperture voltages applied by the
programmed modulator during the first of the 49 electronic scans of
the H. The "plus" potentials as indicated in FIG. 7, allow
electrons to flow through the apertures represented by those
squares and the "minus" potentials represent that at these
apertures, electrons are repulsed and not admitted. When the "first
scan" potentials as shown in FIG. 7 are superimposed on the
electronic image as shown in FIG. 6, it can be seen that there are
electrons to be admitted only at four apertures of the left hand
leg of the H totalling a representative count of 20. There are no
electrons in the image at the location of the other "plus" biased
apertures. This count of 20 is indicated in the first position of
the Hadamard image of FIG. 8, the "20" being encircled in the upper
left corner of the Hadamard image. The count of 20 is stored in
storage means 40. The system proceeds through each of the
succeeding 48 steps. During each of the 49 electronic scans, a
different combination of 16 apertures is biased "plus" to allow
electrons through. The count from each of these electronic scans is
stored and is indicated in FIG. 8.
At this point of the description an analogy will be made to a two
dimensional Hadamard optical filter (i.e. a Hadamard transform slit
mask) shown by FIGS. 9 and 10. This optical analogy of the
electronic biasing of the apertures is made to aid in visualizing
the invention and its operation. Both the optical filter of FIG. 9
and of FIG. 10 overlay FIG. 6, with the filter of FIG. 9 to be
moved in a horizontal direction a step at a time and the filter of
FIG. 10 being moved vertically one step after each horizontal sweep
across the image, to provide the 49 total combinations of the
Hadamard transform being illustrated. The "hatched" portion of the
filters of FIGS. 9 and 10 are opaque, the remainder, light
transmitting windows. The same "first scan" shown by aperture
voltages in FIG. 7 is reillustrated with the optical analogy in
FIG. 11. Two more optical filter examples, that of the 17th scan is
indicated in FIG. 12 and that of the 47th scan is indicated in FIG.
13. It will be seen that the count of 6 from FIG. 12 is encircled
in FIG. 8 and the count of 42 from FIG. 13 is also encircled in
FIG. 8. The optical analogy is illustrative only, the electrical
encoding of the image taught herein being far superior to the
mechanical analogy in a number of aspects including increased speed
of operation and no moving parts.
The 7 .times. 7 Hadamard transform is shown in FIG. 14; the inverse
of the transform S.sup.-.sup.1 is diagrammed in FIG. 15 and the
transpose of the inverse of the transform (S.sup.-.sup.1)T is
diagrammed in FIG. 16. The electron picture which was described in
FIG. 6 and as it appears in the transform of FIG. 8 is now decoded.
The Hadamard image information which has been stored in suitable
storage means 40 is fed to inverse transform means 41 to compute
the inverse transform in accordance with the relation S.sup.-.sup.1
.times. Hadamard image .times. (S.sup.-.sup.1).sup.T = ([N +
1]/2).sup.2 (Input). The inverse transform means may be a computer
programmed with the inverse of the coding matrix. FIG. 17
diagrammatically shows this operation. First in a premultiplication
step the inverse transform S.sup.-.sup.1 is matrixmultiplied times
the Hadamard image FIG. 17a. The intermediate product obtained is
then post matrix-multiplied by the transpose of the inverse
transform (S.sup.-.sup.1).sup.T In FIG. 17 b to provide a decoded
output which is equal to ([N+ 1]/2) (input), where N is the number
of apertures along one row or column of the array. In the example
discussed here, each element of the image is supplying information
to the system for sixteen times as large a fraction of the viewing
time. Thus, the signal-to-noise ratio is improved by a factor of
.sqroot.16 or 4. Use of a large number of apertures would provide a
greater improvement of the signal-to-noise ratio by increasing
still more the efficiency in use of the available scanning time.
The gain in signal-to-noise ratio is given by
G = approximately 1/2 N.sup.1/2
When the required 49 scans have been made of the increment of the
total image which was represented by FIG. 6, horizontal and/or
vertical deflection voltage generators advance the deflection of
the image to the next portion to be considered whereupon the
Hadamard coding and decoding is repreated.
* * * * *